Bottom hole pressure control in well drilling



N. C. WELLS March 26, 1957 BOTTOM HOLE PRESSURE CONTROL IN WELL DRILLING Filed Dec. 20, 1954 INVENTOR. A aeMA/v '6. WELL's,

rrarvey United States Patent O IBOTI'TOMTHOLE PRESSURE CONTROL IN. :WELL DRILL1NG Norman C. Wells, Long Beach, Calif.

ApplieationaDecelnbeli =20, 1954', Serial -N476,-343

'4'Claims. 'T(Cl'. ,2'55-'24) This invention relates.to improved rnethods and apparatus fordrilling wells, andin certain respectsis diit rected to improvements in coperiding (application. Serial No. 43,626, "filed Augustj-ZS, 1951, now Patent No.

2,70l,l'22'issued Feb. 1, 1'955by Donovan BfGrable, on 'Method and Apparatus" Employing fCompressedffGas for Drilling-Wells.

3 In the above entitled application, there. has been dis- "clo'sed-a-unique'methodfor drilling a'wjell, utilizinggas *ratherthanliquid as a circulatingfluid for carrying away the euttings formed in the drilling operation. The drill -'string'uti1ized in this method contains two fluid passages, througha first of which a highvelo'eity gas stream is coniiducted downwardly "to "the" bit 'to' ,entrain the cuttings, and

through =the second of which the'gas and cuttings areithen conducted=upwardly'to the 'surfaceof'the earth; The circul'a'tion fluid -and-cuttings'are"thus 'maintained-out of contact-With the-well bore-wall,asth'eyflowtthrough the string; to thereby avoidcontamination'of'the bore wall or clogging ofthe formation.

' illie/present invention -has todo with the provision, in a system of-the above type, of'improved means for confining the=-gas flow-primarily to the string,'and" for conrolling theflowof materials both from the forma'tionxinto "the 1 well, and-reverseiy from the well into the formation. -Su'chpositivecontrol of flow between the well and formation -during drilling enables use of: the presenfidr'illing system in environments which are extremelvflifiicult to =-drill w.ithconven-tional fluid circulation For instance, withthis'flow control, it is possible-todrill in formations :zwhi'oh are very porous or'hhave low--formatiorrpressures, .-such that there is a decided tendency topless-of circulatt ingwfiuid from then/ell into the formation. in accordl aance ewith the invention, the-i pressure conditions may be so: control-led asito mirn'mize such flow into the formation. ET-0 attain the desired control OFflOW conditions in' 'the well; the invention contemplates the provision in thespace ibetween' the drill string and bore wall at a column of pressurized gas, whose pressure iscommunica-ted bothto Lthe :hit locationand toithe bore-wall. The communicasitionzof that gas pres sure to. the bitacts to-confinethecir- :culating gas stream-essentially todthe interior of "the .string and zto the-actual d'rilling region at the bottom of ::thehole. -Also, the communication of the pressure 90f lithe outerugascolurnn to the-bore Wall-allows for thede- -.sired control of thefiow of-eart-h materials into thewell, {:OI; reverse flow iof' thegas-into the formation. Preferably, it pressure in the outerspace is regula-table, and is maincztainedxin essentially a predete-rmined relationto. the pressurenin:the.:earth:.form ation. 111 most cases,- the"gas*col- .yumu pressure. is maintained:slightlyrgreater than the-pres- .asurezof; 'the.:comrnu-nicating formation, to thus prevent the inflow of sand, fluid, or other materialsi-nto the welhand 1 at ;;the.same .time ,tprevent morefthan a very small-loss of gas to lthCifGlIIlBllG-D. Also, as W-ill-appear, the control of :the pressure intthenouten space serves the a'ddi tionalfunction;0f regulating the rate of; gas-'flowupwardly Within the nstringin; aemannerzalways maintainingasuflicientflow-to jtherater'of gas flow.

ice

' carry'thecuttings upwardly 'without cloggingof the cut "tings in the string.

The circulating gas andouteri'colummof gas-aredesirably inertwith respect'to' the materials encountered in an oil well, and, arepreferably'nrade-up ofsubstantially pure nitrogen. Thisgas-may-"be' circulatedthrough a "closed recirculation system, including a compressor for causing the gas -movement. The pressure'in the outer space within the well-rnay be- -'contr'olled lay-"an automatic 4 regulator valve acting' to respond to" and: co'mp'ensatefor pressure changes in that space. V For maximum simplicity combined with effectiveoperation,- the pressure in the outer space may be controlled bymerely variably: re-

stricting the discharge of the upflowing gas stream from thei'drill1springpasby a pressureregulator responsive to the column' pressure and controlling arestricting'va'lve' in :the recirculation system.

Gas. maybe-addedto'lthe circulating system from time .totime; as'required to compensate for losses of gas tothe formation or to compensate forcontrolled variations-in Thisgas may be added auto-matically past .aregulat'orvalvei -acting to admit additional zgasito'zthesystem when-the gas pressureaha-particular ilooation falls below a predetermined value.

v The invention has-variousadditional. features and ob- -,jects,@ all-:o-f which togetherwith those referred to in--'the foregoing, will be understood tobest advantage-by pro- ,eeeding with a description of certain illustrative methods and fapparatus embodying the invention, as--represented byethez accompanying drawings, in which:

Fig. 1;.is. a-general view illustrating the well drilling system; including-showings ofthe drill string and surface equ p n Eig. 2. is an; enlarged fragmentary section taken 1 longi- "tudin-allythrough the drill. string, including one-of vthe pipe joints and the bi-t',.and

- Fig. 3=is-a cross section on iine-33 of Fig. 2. .-.-Referring'-.firstto the general showing of -Fig.- 1, the

I equipment comprises-a hereinafter described i dual --drill string-generally indicated at-=-10, which-:includes the dr-ive stem or kelly llsextending through 'x-an appropriate head 12 on the casing rlii; thelcasing head preferably being of anyiof various -;known=.types capable of maintaining a ifluidtight-seal with and aboutthe 'kelly 11 during'drilling.

The dri1listring: is rotated by the conventionally illusv ..tratedU-mtarya table 14 through which the kelly I extends ,upnvardlyto v.the.--swivel 15 carryingal-bail l6 by which the drill stringiis verticallysupported as by-=the=conventional,v-equiprnent. i Compressedgas is forced through stringr 10 at. high velocity by means of a compressor at I the,-;surface -of -\,the=earth,-, to: entrain thecuttingspformed .-=in the drilling operation and remove them from :the well. 1 A-regulatorvalve 460 acts to control the" return flow of ,gas from string 10 tothe compressor; in a manner regulating ,the, pressure in the annular space 161 Within the wellziand at the outside of'thestring. A second .regulatorvalve 62 controls the supply of new gas to -the= compressor from a supply '--tank 163. Preferably,

v the, gas circulating systenrisentirely=v closed, and circu- "The? p p ai t 17 d .183 are made upmespeCtively -of I pipe stands 21 and 2210f corresponding length, 'the -standsbeingtenninally and externally upset -at 23 and 124 with :flush or substan-tially straight line "walls at the 1 insides of the upsets. As illustratedin Fig;-2, the stands -are terminally threaded to-form'screwed joints at- 25 and 26 within the upsets, the thread series in each joint having a small taper toward the ends of the pin sections of the joints.

The pipe sections 21 and 22 making up the individual stands may be interconnected beyond the joint ends by suitable means which in eifect integrate the inner and outer pipes, without however, consequentially restricting the passage between them. As illustrative, the pipes are shown to be interconnected by radial webs 28 welded to the inner pipe 22 and secured to the outer pipe by weld metal 29 filled into the slots 39 in the outer pipe which are brought into alignment with the webs initially mounted on the inner pipe. The threads and 26 on the inner and outer pipe are of course in such alinement as to allow for simultaneous making or breaking of both threaded joints by turning one composite stand 21, 22 relative to another.

The swivel head 15, given more detailed description in Patent Number 2,657,016, issued October 27, 1953, may be described briefly as comprising a body into which are connected at gas inlet gooseneck 38 and an outlet gooseneck 39 which are in turn connected to the gas circulation lines. Kelly 11 turns relative to swivel body 35 and goosenecks 38 and 39 during drilling. As will be understood, the swivel serves the function of placing goosenecks 38 and 39 in communication with a pair of inner and outer concentric passages 19a and 20a 1n kelly 11, which communicate respectively with, and are shaped essentially in correspondence with, inner and outer passages 19 and 20 of the string.

The swivel and kelly are so formed that the gas passages therethrough have cross sectional areas which are at least as great as the cross sectional areas of the string passages 19 and 20, so that the flow of gases through the swivel and kelly is as free as through the string.

The dual pipe string 10 carries on its lower end a cutting tool or bit generally indicated at 50, which may be of any of the general types of cutting tools customarily employed, modified and adapted however, to accommodation of the gas circulation in a manner such that the bit cuttings will be entrained in the upflowing gas stream within passage 19. Typically the bit is shown to comprise a body 51 welded at 52 to the lower end of the pipe string and carrying a plurality of bottom cutters 53 extending radially outwardly from a central passage or bore 54. The bit contains a substantially annular fluid passage 55 interrupted only by vertical webs 56 integrating the annular inner and outer portions 155 and 156 of the bit body, passage 55 being so proportioned that its cross sectional area is at least as great as the cross sectional area of the communicating drill string passage 20. Passage 55 communicates at its lower end with openings 57 shaped as illustrated to direct the compressed gas stream discharged downwardly through passage 20 reversely and upwardly within bore 19 of the inner string. As in the case of passage 55, the total cross sectional area of openings 57 traversed by the gas stream will be at least as great as the area of the pipe string passage 20. The bit may contain additional openings 58 extending through the lower portion of the outer annular wall 156 of the bit and serving to place the interior of the bit in restricted communication with the annular space 161 between the drill string and bore wall. This communication is desirably substantially more restricted than the communication through openings 57 between the inner and outer string passages.

Referring again to Fig. 1, compressed gas is discharged from the conventionally illustrated compressor 60 through line 61 and hose 62 into gooseneck 38 to be circulated down through the drill string passage 20 and the bit 50, and then up through the inner string passage 19 to gooseneck 35. The gas then flows through hose 63 to suitable equipment typified by the wet scrubber or separator 64 and closed settling chamber 65 for removing liquid and solid entrainment from the gas stream prior to recirculation to the compressor through line 165. A gas cleaning or scrubbing liquid, such as a suitable mineral oil, may be sprayed into scrubber 64 by pressure developed in a pump 166, which draws clean liquid from the upper portion of settling tank 65. The cuttings and other contaminants separated from the gases settle to the bottom of tank 65, and may be periodically withdrawn through a valve controlled outlet 167. As will be understood, the compressor discharge and return lines (through the separator) constitute a closed recirculation system.

Valve 160, for regulating the gas pressure within space 161 at the outside of the tool string, and for regulating the rate of gas flow through the string, may comprise a conventional diaphragm type automatic regulator valve. More specifically, this valve may include a diaphragm 170 which is subjected at one side to the pressure within space 161 in the well, by means of a line 171 connected into head 12 which forms the seal at the top of the well. Movements of the diaphragm 170 in response to variations of the gas pressure in space 161 serve to actuate the valve element 172 to any of an infinite number of positions within a predetermined range of movement. This valve element 172 acts to control the rate of gas flow through the drill string, and for this purpose is connected into the gas return line from inner drill string passage 19 to compressor 60, preferably being connected into a portion of this line beyond scrubber 64. Valve element 172 serves to variably restrict the flow of gas through line 165, to control the back pressure against the gas stream in the drill string, and to thereby vary the pressure within space 161.

Gas is added to the closed circulation system from a supply tank 163 in which the gas (preferably nitrogen), is maintained under substantially greater pressures than occur in line 165. The make up gas flows into line 165 at a point beyond valve element 172 under the control of the automatic pressure regulator valve 162 whose diaphragm 174 is subjected to the gas pressure at the suction side of compressors 60. As will be understood, if the gas pressure at that location falls below a predetermined value, valve 162 automatically opens to admit sufiicient additional gas to the closed system to again obtain the desired pressure at the downstream side of valve 162.

In considering the operation of this system, assume the equipment to be set up as illustrated in Fig. l, with the compressor 60 operating to discharge compressed substantially pure nitrogen through line 61 into gooseneck 38. The gas flows downwardly through the swivel, Kelly passage 20a, string passage 20, and bit passage 56 into bore 54 and the inner drill string passage 19. With the bit being rotated to drill the formation, the cutters 53 progressively disintegrate and penetrate the formation and form cuttings at the locations of openings 57. By reason of'the high velocity gas flow at its point of reversal within the opening 57 (as permitted by the open condition of the circulating passages within and throughout the drill string) the cuttings are entrained in the gas stream and carried thereby up through passages 19 and 19a and gooseneck 44 into the separator 64. Even in the drilling of deep wells, it is possible to maintain within passage 19 a gas velocity, preferably at least about 1500 feet or above per minute, suflicient to assure continued entrainment of the cuttings throughout the course of the gas flow to the ground surface. From separator 64, the cuttings and scrubbing liquid, as well as any other contaminants picked up in the well, are taken to the closed settling tank 65, from which the contaminants are periodically withdrawn.

Regulator valve 160 is adjusted to automatically maintain a predetermined pressure in the annular space 161 between drill string 10 and the well bore wall. That pressure is desirably so regulated as to maintain a predetermined relation between the pressure within space erase 5. p161; and thepressure of;the:surrounding forniation, 175 a whichcommunicates with rt-he well; ;:the. irelations-bflWflfi thesetwo pressures :being :su'chgas ;to :attain -;optimum;con-

ttrol:of-. thercirculating gas and formation materials under 6 :LsfO whichmalverlfith-hasrbeeir set. A reverse-:actiomof curse aoecurs, iii the spressurea within 'spacei; 161 becomes greaterethan-tthe: desired? pressure, cvalve 160::then acting .-,;to;- decrease lthe -.restr iction;in: line 51165; thereby increasing vthe particular: drilling. conditionsziwhich; are;- encountered. 5 :uthemrate; ofsflowathroughntheidrillzstring-passages :and

Under; most ;circumstanc es,: it ris; desirable; that the :pressure-within therspace; ,161: :;be .-1naintained*:approxirnately equal: to, thencommunicating: pressure in. :thecsurrounding formation. 175,; so.;that tthegpressurized gas 'within :space from? flowing. into i 'theswell. aysincelit; isuusually rather diflicult to maintain the pressure;inrspace;:t6lrrexactly equal to the pressure in the formation, and since it is usually desirable to prevent the-iiifiow of materials into .-:tendingstosdecreasezthe apressurea within space: .161 to; the esiredrvialue Undensome operatingconditions; .as,:where rather; pressure; 7111f space. r161:v is; slightly greater I than; the 1 formation pressureptheretsmay be a normal substantially -1161.wilLact:to:maintainathexformation;fiuids;;sand;;etc.,i; -;10 tcontinuous flowa-of; arsmall amountzof.the:,circulating gas throttghybit; passagesu58: :intoaz'space 1161: and then into the formation, with the actuation. of ,valve 160 ,serving' to regulateEthat.ratebfzflow:,to.;maintain arrproper .pressure in -tsspaee. 161. ;,=Similar ly, it-is:zconc.eivableithat:unden some the well frorrrzthe formation 'everrfatrther expense of loss-i515:.;openati:ngiconditionsdthere mightbe axsmallfiowjofimate- ,of.some of..the circulating gas, I prefento regulate valve .1160 for. maintaining'the pressureiin space .161. slightly greater than'the" formation pressure '(though still being approximately equal ':to -that'-pressure)- so that any flow rial:into the drill-rstringfrom spaceylfil. .It isdesi'rable 1; that the flow ;through passages 58;:be; kept at a minimum, ..-.th. eraci hig ue o i ytgasfi wr z strin an nstan-tial-ly noggast-fiow in spacer-161 at-the outside ,of

which maytoccur will comprise; afshghtz flow; of; gas from3ii-20, the.-.strir1g, sorthat the-rdifierence inayelocity. at the inside space 161 into the formation rather than a reverse flow of the formation materials into the well bore. In most cases, the pressure in space 161 may for this reason be between about 5 and 50 pounds per square inch greater than the pressure in the communicating formation, a preferred value for this pressure differential being about 10 pounds per square inch. Such maintenance of a slight excess of pressure within space 161 also assures maintenance of a gas column within space 161 throughout its entire vertical extent, that is, all the way from head 12 downwardly to the bottom of the bore so that this gas column communicates directly with the interior of the bit through bit passages 58. In order to determine what the formation pressure at 175 is, to thus determine a proper setting for regulator valve 160, compressor 60 may be first actuated to a condition developing a substantially greater pressure in space 161 than could be expected in the formation, following which the compressor may be stopped to allow the excess pressure in space 161 to slowly bleed off from the closed circulation system into formation 175 and until the decrease in pressure ceases by reason of the equalization of pressure in space 161 and the formation. The pressure in space 161 may then be read from a gauge 176 connected into line 171, and that pressure reading will correspond to the formation pressure, minus the relatively small pressure exerted by the column of gas in space 161 as a result of the weight of the gas. Valve 160 may then be adjusted to maintain a pressure in space 161 having the desired relation to the determined formation pressure, say about 10 pounds per square inch more than that pressure.

To describe now more specifically the actual manner of functioning of pressure control valve 160, assume first that the drill and other apparatus of Fig. 1 has been operating with the gas pressure in space 161 maintained at the value for which regulator valve 160 has been set, and that the pressure within space 161 then commences to drop beneath that value (usually because of a loss of some of the gas to the formation). This drop in pressure within space 161 is communicated through line 171 to the right hand side of diaphragm 170 in valve 160, with the result that the diaphragm is actuated in a direction for slightly increasing the restriction which it offers in line 165. This increased restriction causes a slight increase in back pressure in the scrubber, line 63, gooseneck 44, and in upfiow passage 19 within the drill string. Consequently, the return or upward movement of the high velocity gas stream within the passage 19 is slightly decreased, and the resultant increase in pressure within the bit at the bottom of passage 19 causes some of the circulating gas to flow through bit passages 58 into the outer space 161, in an amount suflicient to raise the gas pressure within the space 161 back to the desired value and outside of the string results in the maintenance of a slightly greater gas pressure at the outside of the string than at its inside, even though there is direct communication between these locations through passages 58.

In the event that the cuttings within gas upfiow passage 19 in the string accumulate to an extent introducing a danger of clogging that upfiow passage, the excess of cuttings causes a slowing of the upward movement of the gas stream within passage 19, which slowing results in an increase in pressure in the passage and in the comher of cuttings and prevent clogging. Thus, valve 160 serves the secondary function of automatically regulating the rate of gas flow through drill string 10 in a manner assuring handling of the cuttings, and compensating for any changes in the rate of cutting formation.

I claim:

1. Well drilling apparatus comprising a drill string, a bit carried at the lower end of said string and adapted to form cuttings at a bottom location in a well bore, said string containing a first passage adapted to conduct a high velocity gas stream downwardly through the string to said location to entrain said cuttings, said string containing a second passage for then conducting said stream and cuttings upwardly to the surface of the earth, means for producing said high velocity flow of said gas stream through said passages, and means operable to maintain a pressurized column of gas in the well between said string and the bore wall with the pressure thereof communicated to the bit at said bottom location and to the bore wall, said last mentioned means comprising an automatic regulator valve responsive to said gas column pressure and acting to automatically regulate the rate of discharge of said upfiowing gas stream from said second passage in accordance with changes in said column pres sure and to thereby regulate the column pressure.

2. Well drilling apparatus as recited in claim 1, including means forming a closed recirculation system for said gas stream at the surface of the earth.

3. Well drilling apparatus comprising a drill string, a bit carried at the lower end of said string and adapted to form cuttings at a bottom location in a well bore, said string containing a first passage adapted to conduct a high velocity gas stream downwardly through the string to said location to entrain said cuttings, said string containing a second passage for then conducting said stream and cuttings upwardly to the surface of the earth, means for producing said high velocity flow of said gas stream through said passages, means operable to maintain a pressurized column of gas in the well between said string and the bore wall with the pressure thereof communicated to the bit at said bottom location and to the bore wall, said means for maintaining said gas column including an automatic regulator valve responsive to variations in said column pressure and acting in accordance with said variations to automatically variably restrict the flow of gas discharged from said second string passage, there being means forming a closed recirculation system for said gas stream at the surface of the earth, and means for adding gas to said closed system and including a second automatic pressure regulator valve operable to add gas to the system in response to a pressure drop in said system beyond said first valve.

4. Well drilling apparatus comprising a drill string, a bit carried at the lower end of said string and adapted to form cuttings at a bottom location in a well bore, said string containing a first passage adapted to conduct a high velocity gas stream downwardly through the string to said location to entrain said cuttings, said string containing a second passage for then conducting said stream and cuttings upwardly to the surface of the earth, means for producing said high velocity flow of said gas stream through said passages, and means operable to maintain a pressurized column of gas in the well between said string and the bore wall with the pressure thereof communicated to the bit at said bottom location and to the bore wall, said last mentioned means including an automatic regulator valve responsive to variations in pressure at a location communicating with said gas column and acting to automatically regulate the rate of discharge of said upfiowing gas stream from said second passage in accordance with said pressure variations and to thereby regulate the column pressure.

References Cited in the file of this patent UNITED STATES PATENTS Nolan Dec. 27, 1921 Grable Feb. 1, 1955 

